Sewage treatment process and apparatus



Nov. 21, 1944. J GUN- 2,363,176

SEWAGE TREATMENT PROCESS AND APPARATUS Filed Aug. 11, 1941 IN VENTOR.

Patented Nov, 21, 1944 AT N OFFICE 2,363,116 'snwacn 'rnaa'rman'rraocnssAND l APPA BATIK Johanna Gun z, Chicago, 111., "assignor to InfllcoIncorporated, a corporation of Delaware I Application August 11, 1941,Serial No. meats 1 mcisinis.

Thisinvention relates to the biological treatmerit of sewage, industrialwasteand other impure liquids and particularly to the treatment ofmunicipal sewage. More specifically, it relates to the treatment of suchliquids .by what is generally'called the activated'sludge process.

It is a principal object of my invention to sim i plify such processandto cut down its cost considerably.

, It is anotherobject of myinvention to improve the operation of anactivated sludge plant it by a ,newcombination of biological treatment,1

dilution and sedimentation.

i Another, object is to improvethe activity of i the microorganisms)favorable for the process while preventingthe g'rowth ot largenumbers.of unfavorable microorganisms.

Still another object is to provide a flexible system which, can readily.be adjusted to the varylung conditions of the sewage flow and to thevarious standards of purification requirements.

A still further object is to improve the removal ,of sewage solids bysedimentation.

l The activated sludge system oi the prior art generally provides a,primary settler, an aerator and a flnal settler, the'flow oi the sewagebeing a through the three tanks inthe sequence as statp, ed. The majorpart of the sludge separatedin the finalsettler is returned to theaerator as socalled "return sludge, whilethe minor part,the

so-calle'd fexcess sludge,.j (because it is in excess, .ofrwhat can bere-used. in the aerator) ,.18 either sentdirectly to waste or passedback into the primary settler where it mixes and settles togetherwiththe raw sludge settling therein.

The requirement of three large ltanks for the several steps of theprocess, each of which needs large. and intricate equipment, makes; thecon ventional activated sludge process very expensive. It is one of theobjects of my invention to eliminate one of the successive steps oftheproc ess and the tank needed for it and thereby to considerablysimplify the process and out down the original cost 01 the treatingplant and also i the expense of its operation, a

One of the main drawbacks. of the 1 activated sludge process, is that itrequires a settling period of at leasttwo hours in the. final settler;

7 Frequently considerably longer detention periods are usedbeforethesludge is returned fromlthe final settler to the aerator Duringsuch settling and storage periods the sludge is deteriorating rapidly byanaerobic action. Such action, which is due to thepresence ofmicroorganisms oi the anaerobic orseptic lrind, is self starting underanaerobic conditions and is directly opposed to the aerobic biologicalaction of the aerator,,which is required for that process. Thedeterioration of the sludge is sometimes carried so farthat the Isludgehas to bereactivatedat considerable-eir pense for equipment andpower, before it can be used again in the aerator. Itis oneot theprincipal objects of my improved process to overcome such-dimculties andtodo away with such settling and storing and their bad eiiecton theprocess. p i, The primary tank or a conventional activated sludge planthas to provide isuflicient. capacity for. the treatmentoi the maximumflows. At .night'and at other times of low sewage how the primaryqtankcontains a, stagnant body of sewage. This sewage, as well as the sludgesettling from it, tends to become septic and a large amount of suchsepticmaterial enters the aera- 20 tion tank upon resumption of normalflow, thus seriously affecting the conditions therein. It is man objector my improved process to have a large andcontrollable flow through thepreliminary'tank at all times. and to provide for great Still otherobjects of my, invention will appear from the following detaileddescription of my improved process. v p i a More specifically, I proposeto carry out an activated sludge process in a treatment tank and anaerator but without any final settler following the aerator fortheseparation of the activated sludge and the clarified supernatant fromthe mixedaerator liquor. Whereas such final setpart or the process Ihave found thatthe process can beoperated without a final settler withas satisfactory, and in some'respects with better.

In my process theraw sewage flows into the treatment tank together witha large body of fresh previously aerated liquid. This body of liquid haspreviously passed through the aerator and is rich in active aerobicbacteria and in solmineralized by the action oi' the bacteria. A

reat part oi the aerobic treatment whichiin the conventional processiscarried out in the aerator 1 is taken over inrny process by thetreatment tank while the llquid undergoes clarification. I Moreover,instead of providing the aerator with a sludge which has been settledand stored for several hours and as a consequence or such settling' andstoring lost much of its ability to purify the sewage to be treated byit, I send mm the quantitiesof active aerobic material in said tank. i

tler hasheretoiore been thought an essential forminga powerful aidtherefor.

aerator a mixture of freshsewage and freshly aerated solids and Iwithdraw such mixture from the treatment tank at a point where itssolids content is of proper concentration for the further treatment inthe aerator. The conditions in the aerator-of my process are thus muchimproved in various respects over those in an aera tor of an activatedsludge plantv as heretofore known. I The sewage entering the aerator isalready, to a considerable extent, pretreated by as a motor 2| and areducer 22. As is also comthe mixing of the entire aerator eilluent withraw a sewage, whereby there is secured a large amdiint' of activeaerobic bacteria in the treatment tank.

Great quantities of such bacteria reenter the aerator in admixture withthe sewage to be treated as I establish a continuous circulation betweenthe treatment tank and the aerator of a magnitude which is a multipleof. the throughput flow, and these bacteria enter the aerator beforetheir activity has been reduced bysettling and storing. Furthermore, inthe conventional process, clarified eflluent'of a preliminary settlerand settled sludge ofa final settler are passed into the aerator and thesettled sludge has to be re-suspended and kept in suspension in theclarified eflluent. It is well known that monin an apparatus of thistype, I prefer that sewage to be treated be introduced into a centralloading well 23 which may comprise an open-end cylinder or other baiiiemeans descending within the tank and adapted to direct the flow ofincoming liquid downwardly.

The clarification chamber of my apparatus will differ from thatcustomarily used in that mine provides a third withdrawal conduit 24adapted to remove a large portion of liquid from the clari- I ilcationtank together with a major portion of the finer suspended particlescontained therein.

For this' purpose I show a partition 25 provided with a plurality ofinlets 26, preferably extending around the diameter of the tank so thatsolids and liquid are withdrawn from all portions pf the tank. It willbe obvious .to those skilled-in the art that other suitable withdrawalmeans can be provided within the clariiier ill, it being understood thatit is desired to withdraw alarge portion of liquid with a large portionof the finer 1 suspended solids which .will be contained therein.

it is difilcult and requires much time and. power condition'once theyhave'been allowed to settle .out of the liquid, and that such solidseven when re-suspended have lost much of their capacity as flocculatingmeans. I, therefore, save power and detention time and I improveflocculation in the aerator by providing it with a suitably concentratedsuspension of pretreated sewage containing activated solids.

In a similar way the conditions-in the clarification tank of my processare superior to those in a preliminary settler of the usual activatedsludge plant. Th clarification is improved, the large mass ofrecirculated mixed liquor with its rich contents of well-flocculatedsuspended solids time the recirculation flow canbe adjusted to the flowconditions of the raw sewage so that even at the times of lowest sewageflows there, will arise no stagnant condition causing septicity. Septicconditions are furthermore prevented in the treatment tank by the massof active aerobic her I i, which may be of any suitable sire or shape,

such as a basin with a vertical wall Ii and the gently sloping bottomI2. The, clarification chamber may be similar to those ordinarily usedin that it is provided with aneiiluent launder l3;

"communicating with an" 'eilluent conduit 14, for removal of clarifiedliquid from the system. Prefierably, theclariflcation chamber will beprovided with sludge. rakes 15, suspended from a shaft'it ,by anysuitable means such as braces I'Land adapted to move sedimented solidsto a slud e sump il in thefloor l2. A sludge conduit 18 leads 'fromthesludge sump l8 and is provided with a valve 20 to control-the removal ofsedimented solids to waste. The shaft l6 of the raking mechanism can berotated by any suitable mea s, such At the same to resuspend solids andkeep them in a proper The third withdrawal line 24 maybe providedwithany suitable valve 21 and leads into an activated sludge 'aerator'iil,The aerator'may comprise the customary tank provided with side walls 3|and hopper bottom 32. The aerator, or activator as it is commonlycalled, is also provided with an eflluent launder 33, communicating withan eilluent conduit 34. In the central part of the basin I provide acustomary circulator and v agitator means which may comprise an updrafttube as in spaced; relationship to the bottom of the tank and s pportedby any suitable means, such as legs 36.v In theupperportion of theupdraft tube is an impeller 31, driven by any suit able means such asamotor 38, to cause a circulation of liquid upwardly throughth'e drafttube,

from whence it is sprayed over the surface of the liquid within theaeration tank 30.

The efliuent conduit 34 is preferably. provided with a pump 40 and leadsto a mixing chamber II. 'A raw sewage conduit 42 likewise dischargesinto the mixing chamber ll in which the emuent from the activated sludgeaerator and the raw sewag are thoroughly mixed. The mixture then passesthrough conduit 43 into the loading well 23 of the clarificationchamber.

. The operation of the apparatus will be'readily understood. Incomingraw sewage and effluent from the activated sludge aerator are mixed inv, amount of finer suspended solids is withdrawn '60 the mixing chamber4i and pass into the loading i well 23 'ofthe clarification chamber 10.v In the clarification chamber the heavier solids settle to the bottomwhere the'yla're scraped to the sludge sump l8 and withdrawni' throughthe conduit is. A large portion of the liquid containing a large throughthe conduit 24 continuously andpasses into the activated sludge aerator30. In the aerator the liquid is subjected'to the usual-aerv.

tion process for a considerable period. As 'iscommon in the activatedsludge process; I prefer? that the average retention time in the aeratora be suflicient to providefor'adequatepuriflcation -of the liquid. Partof the liquid in the activated sludge aerating chamber Silis withdrawncontinuously and mixed with more raw sewageg'and the treatment repeated.Clarified liquid from the clarification tank is withdrawn throughconduit It to waste.

It will be noted that T provide no secondary clarification chamber as iscustomary in'the prior art. I. return all of the aerator emuent'tofthef7. The improvement in the activated sludge process of treating sewagethat resides'in returning the unsedimented eflluent from the aerationzone to the inlet of the primary clarification zone to pass againthere'throug'h with entering raw sewage, whereby the raw sewage is givena prolonged initialactivated sludge treatment in said clarificationzone, withdrawing sewage from one point in said clarification zone whilestill containing a substantial amount of activated sludge suspendedtherein and passing this withdrawn sewage into and through the aerationzone, withsaid clarification zone. withdrawing sewage from one level insaid clarification zone,said withdrawn sewage containing substantialamounts of suspended activated sludge solids, passing the withdrawnsewage and contained solids into and through an aeration zone, returningthe aerated mixed liquor issuing from said aeration zone .to

the primary clarification zone to eflect said dilu tion and primarytreatment of raw sewage,

9. In-the activated sludge process of sewage treatment wherein sewage isfirst passed through a primary settling zone, then aerated in admixturewith activated sludge in an aeration "zone,

and the aerated mixed liquor then clarified, the improvement whichresides in providingthe activated sludge for the aeration zone byreturning all the aerated mixed liquor from the aeration zone to theprimary settling zone and passing partly settled sewage containingactivated sludge I solids in suspension from one level in said primarysettling zone into said aeration zone, withdrawing to waste all thesludge which is being wasted-in the process from another level in saidprimary settling zone, and withdrawing to waste clarified liquid fromstill another level in said primary settling zone.

withdrawing clarified sewage to waste from another level in saidclarification zone, and'withdrawing deposited solids from a third levelin said clarification zone.

10. In apparatus for the treatment of sewage by the activated sludgeprocess including a settling tank, a raw sewage inlet into said settlingtank. a sludge outlet from the lower part of the settling tank, aclarified sewage outlet from the upper portion of the settling tank. anactivated sludge aerator, an inlet into said aerator, and means in saidaerator for aeratingsewage during its passage therethrough: a thirdoutlet froman intermediate portion of the settling tank communicatingwith said inlet into the aerator, an outlet from the aeratorcommunicating with the said raw sewage inlet to the settling tank, and

pumping means for causing continuous ilow of sewage from said settlingtank to and through saidaerator and back to said settling tank.

JOHANNA GUNZ.

